Kenyan pregnant women have been warned by scientists from the University of Michigan not to believe creams and ointments that promise to prevent or reduce stretch marks because scientists are still learning about what causes them in the first place.

"Most of the existing products are not based on solid scientific research," said Frank Wang, M.D., assistant professor and dermatologist at the University of Michigan Health System. "Very few to none of the items said to prevent or fix stretch marks really work."

For the research, the scientists studied skin samples from 27 pregnant women who had recently-formed stretch marks, comparing the stretch mark skin to both nearby stretched skin on the abdomen and to less-stretched skin on the hip.

They found the elastic fiber network in the dermis gets disrupted in a stretch mark. “After giving birth, this network remains disrupted. Elastic fibers give skin its elasticity, or the ability to "snap back," after stretching. The skin tries to repair the disrupted elastic network but it does not appear to be effective, which in turn promotes the lax, loose skin seen in more mature stretch marks.”

Stretch marks affect 50 percent to 90 percent of women but present research for treatment options does not find anything currently available to effectively repair those disrupted elastic fibers.

"It may, therefore, make more sense to focus on preserving the elastic fibers you have rather than repairing damaged ones within stretch marks," Wang said. "Regardless, it's more complicated than just rubbing something on your stomach."

For Susan Njoki, a mother of a four month baby, she finds stretch mark lotions really helpful. “When I was pregnant, I used stretch mark lotions religiously,” she said, “it did not get rid of them but it reduced their appearance, which is better than having my stomach covered in stretch marks.”